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The Broad Picture
We see as we progress from the parallel placements (Au/Ge) through the table to (Ag/
Si) and finally to (C/Cu) where we have run out of slots, we progress from AI to AI and
finally Life (C/Cu). But what does the fine electric conductor of AI, which is Cu, have to
do with carbon and biological life?"
The biochemistry of all terrestrial life seems to be similar throughout the spectrum of
species, and so much so that it would seem we all descended from a common
ancestor. Of course at the most fundamental level life as we know it is based on
carbon. This is because it has 4 valence electrons allowing it to combine in long chains
with hydrogen called hydrocarbons, and combine readily with oxygen 2-, and nitrogen
3-. Biologist have hazarded to look at silicon as a candidate since it has a valence of 4
as well, and came to the conclusion that life did not form like this because in the
presence of oxygen it readily combines with it making SiO2 silicon dioxide the basic
ingredient of sand. Perhaps many different organisms originated differently and
independently but at some point we may have a common ancestor. Her name is LUCA
(Last Universal Common Ancestor). Using a comparative approach biochemists have
traced our ancestry back to LUCA who shared the traits we have today. Some of these
traits are she stored her genetic information in DNA, and made use of the same twenty
amino acids we use to make our proteins with the same RNA machinery and genetic
code we use."
However, in dating LUCA we looked at the metabolic pathways common to all of life
and found her metabolism was based on iron (Fe). In today’s oxygen rich environment
iron quickly oxidizes to its ferric state and is highly insoluble. It is believed then that
LUCA lived before the earth was rich in oxygen. Today we use in our metabolic
pathways copper (Cu) because its oxidized state is more soluble than its reduced
forms. Marine organisms use iron and it is the limiting nutrient in the ocean and the
marine organisms have developed mechanisms with which to to extract iron form
bacteria. But the important point here is that the earth became oxygen rich with the
arrival of photosynthesizers, plants that could use energy from the sun to make
electrochemical energy (sugars) from carbon dioxide and in the process make oxygen.
The oxygen rich atmosphere seems to have happened about 2 billion years ago but the
evidence for life on earth goes back as far as 3.5 billion years, putting LUCA’s age in a
wide gap of 2 billion to 3.5 billion years old.$